Field of the Invention
The present invention relates to an image processing technique in a mixed reality technique.
Description of the Related Art
As a technique for seamlessly merging a real world and virtual world, so-called MR (Mixed Reality) techniques are known. As one of the MR techniques, a technique which uses a video see-through HMD (Head Mounted Display) is known. In this method using the video see-through HMD, a video camera or the like captures an image of an object, which nearly coincides with that viewed from a pupil position of an HMD user, and the HMD user can view an image obtained by superposing a CG (Computer Graphics) on the captured image.
In the video see-through HMD, a charge-coupled element such as a CCD captures an image of an object to obtain digital image data of that object, and a CG image is superimposed on the captured image to generate an MR image (mixed reality image). Then, the generated MR image is displayed for the user via a display device such as a liquid crystal display or organic EL display. FIG. 30 shows a state in which the HMD user wears an HMD 3001. Although not shown in FIG. 30, an external apparatus is arranged in addition to the HMD 3001, and the HMD 3001 transmits position and orientation information of itself to the external apparatus. The external apparatus superimposes a CG on a blueback image based on the position and orientation information received from the HMD, and transmits that image to the HMD. The HMD superimposes the CG image received from the external apparatus on a captured image captured by the HMD, and displays that image. In this manner, the HMD user can experience an MR space using the HMD 3001.
Upon superimposing a CG image and an image captured by a camera, the CG image is often translucently superimposed on the image. For example, when the CG image includes an object such as a window, it is translucently chroma-key-combined with a camera image. By translucently chroma-key-combining the CG image, the HMD user can view a video as if an actually captured image were existing outside the window. In this case, a coefficient, which is required for translucent processing, is called an α value, and represents a transparency, is required in addition to the CG image.
FIGS. 31A to 31C show such example. FIG. 31A shows an image captured by a camera, and FIG. 31B shows a CG image. Reference numeral 3103 denotes an area which is translucently chroma-key-combined with the captured image; and 3102, an area where the captured image is replaced by the CG image when they are chroma-key-combined. FIG. 31C shows a chroma-key-combined result of FIGS. 31A and 31B. Since the area 3103 in FIG. 31C undergoes translucent chroma-key combination, the camera image is translucently displayed on this area.
In order to chroma-key-combine images acquired from different apparatuses like the HMD and external apparatus, a translucent area has to be separately transmitted as information. Japanese Patent Laid-Open No. 2005-107780 describes a method of reducing data of an α value by embedding the α value in image data.
However, since the technique described in Japanese Patent Laid-Open No. 2005-107780 embeds the α value in data of an image, color information of the image is smaller than that before the α value is embedded.
The present invention has been made in consideration of the aforementioned problem, and provides a technique for identifying a translucent area and information indicating its transparency without reducing an information amount of an image in association with a CG image including the translucent area.